Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$103.39	5.129%	$108.6929	$108.69	$108.70	$108.70
Purchase #2	$215.73	4.351%	$225.1164	$225.12	$225.10	$225.10
Purchase #3	$66.78	8.658%	$72.5618	$72.56	$72.55	$72.60
Purchase #4	$165.25	12.297%	$185.5708	$185.57	$185.55	$185.60
Purchase #5	$73.72	6.869%	$78.7838	$78.78	$78.80	$78.80
Purchase #6	$85.55	6.760%	$91.3332	$91.33	$91.35	$91.30
Purchase #7	$18.68	10.613%	$20.6625	$20.66	$20.65	$20.70
7 purchase totals =	$729.10		$782.7214	$782.71	$782.70	$782.80